Deposition of films on a substrate surface is an important process in a variety of industries including semiconductor processing, diffusion barrier coatings and dielectrics for magnetic read/write heads. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are two deposition processes used to form or deposit various materials on a substrate. In general, CVD and ALD processes involve the delivery of gaseous reactants to the substrate surface where a chemical reaction takes place under temperature and pressure conditions favorable to the thermodynamics of the reaction
However, there lies a great challenge where deposition is desired only in certain areas of a substrate surface. Typically, such a result is achieved by depositing a continuous film and patterning it using subsequent lithography and etch steps. Such processing is time consuming and expensive, and does not offer the precision required for many applications. One possible solution is the use of selective deposition whereby the material is deposited only in the desired areas thereby eliminating the need for subsequent patterning steps. Existing methods for selective deposition, however, generally suffer from high levels of defects. These defects can take the form of deposition in undesired areas (i.e., the process is not truly selective), and/or the absence of deposition in desired areas. Many processes cannot tolerate these types of defects. Furthermore, a selective deposition process requires a certain throughput and selective growth rate to be commercially viable. That is, a commercially viable process would require relatively rapid processing steps, as well as rapid environmental changes between individual processing steps. Yet another concern is that there is often a certain level of orthogonality required in a selectively deposited feature. Mushrooming into adjacent features may interfere with later processing steps and/or the performance of the semiconductor device.
One example of a commercially useful process is selective epitaxy. In selective epitaxy, a semiconductor is grown selectively on a semiconductor substrate relative to an insulator substrate. Selective epitaxy is achieved by using both a deposition gas and an etch gas in the same process at the same time. It exploits the fact that nucleation occurs more readily on the crystalline substrate than on the insulator, as well as differences in the etch rate of material deposited on the semiconductor versus the insulator. However, this process is limited to epitaxial processes.
There is thus a need for methods for selectively forming films over only certain parts of substrate surfaces without one or more of the problems discussed above.